The present invention relates to lead-free solder powder material, lead-free solder paste, and a method for preparing same. More particularly, the present invention relates to lead-free solder powder material having good wettability and a low melting point, lead-free solder paste including such solder powder material, and a method for preparing both.
As is known, lead (Pb) is included in many conventional solder alloys. Further, an increasing number of microelectronic devices are prepared by a process using the aforementioned alloys. For environmental reasons, many countries are planning to mandate the exclusion of lead in soldering and other processes at some near future date. Therefore, it is highly desirous to provide a solder alloy free of such lead.
Accordingly, several kinds of lead-free solders are now being developed. These lead-free solders, however, are typically difficult to be effectively used in most manufacturing processes, due primarily to low wettabilities and higher melting points than known (tin-lead) solder alloys.
Various solder alloy compositions, including lead-free types, and processes using same are described in the following patents:
In addition to the foregoing, a method other than a gas atomizing method is described in Laid-Open Japanese Patent Publication No. 3-169500, wherein powder material of predetermined composition and small balls are put in a pot, which is then filled with inactive gas, sealed and rotated. The powder material is mechanically milled by the small balls. This method is mainly used to impart heat-resistance and thermal durability to solder powder material by mixing intermetallic compounds having high melting point with Snxe2x80x94Pb alloy to make solder powder material. The method is acceptable in that it can prevent the solder powder material from forming large grains and that it does not require heat to melt the powder material during the preparation.
Recently, the use of intermetallic compounds in microelectronic products and processes having high melting points in turn appear to necessitate the use of solder alloy including lead. The aforementioned disadvantages caused by lead cannot be avoided, so it seems, when manufacturing such products. As will be defined hereinbelow, a solder powder material essentially free of lead has been developed which can be effectively used in a manufacturing environment, including particularly one wherein microelectronic products are made. Such a solder possesses both high wettability and a low melting point. It is believed that such a solder will constitute a significant advancement in the art.
One object of the present invention, therefore, is to provide excellent lead-free solder powder material having a low melting point and high wettability when formed into a solder alloy.
Another object of the present invention is to provide lead-free solder paste including such lead-free solder powder material.
Yet another object of the present invention is to provide a method for preparing such lead-free powder material and paste materials.
According to one aspect of the invention, there is provided lead-free solder powder material of metal powder material comprising a combination of two or more metals capable of forming an intermetallic compound, wherein the metal powder material includes an amorphous phase and an unreacted phase of the combination, which is a prior state to forming an intermetallic compound. Please see hereinbelow for definitions of said phases.
According to another aspect of the invention, there is provided a method for preparing lead-free solder powder material comprising the steps of positioning powder material of two or more metals capable of forming an intermetallic compound and small metal balls in a sealed container and moving the metal balls in the sealed container to finely grind the powder material of two or more metals, thereby obtaining a metal powder material including an unreacted phase and an amorphous phase.